Facebook is a free-access social networking website that is operated and privately owned by Facebook, Inc. Users can join networks organized by city, workplace, school, and region to connect and interact with other people. People can also add friends and send them messages, and update their personal profiles to notify friends about themselves. The website's name refers to the paper facebooks depicting members of a campus community that some US colleges and preparatory schools give to incoming students, faculty, and staff as a way to get to know other people on campus.

Mark Zuckerberg founded Facebook with fellow computer science major students and his roommates Dustin Moskovitz and Chris Hughes while he was a student at Harvard University. Website membership was initially limited to Harvard students, but was expanded to other colleges in the Boston area, the Ivy League, and Stanford University. It later expanded further to include any university student, then high school students, and, finally, to anyone aged 13 and over. The website currently has more than 175 million active users worldwide.

Facebook has met with some controversy over the past few years. It has been blocked intermittently in several countries including Syria and Iran. It has also been banned at many places of work to discourage employees from wasting time using the service. Privacy has also been an issue, and it has been compromised several times. It is also facing several lawsuits from a number of Zuckerberg's former classmates, who claim that Facebook had stolen their source code and other intellectual property.